Any article, image, and spreadsheet that is placed on a layout (and stored in Enterprise) can be highlighted when viewing the layout in fullscreen mode or in the Publication Overview Application. The color used is the color of the Workflow status that is assigned to the object.
This gives a good overview of how far the layout and the publication as a whole is progressing.
Enabling or disabling this feature is done through the menu in the top-right corner of the page.
Figure: Articles and images highlighted in the Publication Overview application.